How To Get 2 Routers Talking To Each Other

One way to look at the Internet is to see it as a bunch of circuits connecting a bunch of routers. A single circuit connects two routers. Once you've designed your network then you have to build it and see if it works. One circuit will be tured up first. Let's examine that first circuit.

The circuit can get quite complicated by itself but let's leave all of that up to the physical layer guys and just wait for them to tell us it's ready. We know where our two routers are and we ordered the circuit to connect them. When they tell us it's ready we'll plug in our routers and see if they can see each other.

Let's say our circuit is an OC48 over DWDM. In our routers we have POS interface cards. Step one is I put a software loopback on the interface card of one of the routers facing the other router.

R2#conf t
R2(config)#int pos 4/5
R2(config)#loopback network line

Then we show the interface of the other router and see if it is up/up (looped). We also give it a good little test to see if we can ping our own IP address.

R1#show int pos 5/4

up/up (looped)

ping 12.13.14.15

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Once we are able to do this we can then release the physical layer support guys. If we can't do that then we need to hang on to the physical layer transport guys for awhile.

Once we can ping to a loopback from the far end router then the fun begins. Now we go to work on network layer 3 stuff.

Since I am a rank beginner in network layer 3 stuff I will hack along on this article as best as I can hoping to learn a few things along the way. I sure wish I had a nice Dynamips router emulator window to get some nice copy and paste command outputs on here but that will have to wait for another day.

We'll go with Cisco routers since I don't know much about Juniper or any other router.

We'll go with Packet Over Sonet interface cards.

But here is where we get some confusion. Our circuit is DWDM and yet we're going to use Packet Over Sonet (POS) interface cards. I think POS interface cards can be used with DWDM or SONET. In fact I am pretty sure of this. So we'll go with POS interface cards.

Now we have to make all of the layer 2 settings match on both ends. Bandwidth, CRC, scrambling, timing, etc. Once each router can ping the other router then we're on our way.

We could have two LAN's connected in this fasion. And there we would have a network I suppose. But we're missiong our ISP at this point. And we have yet to discuss topology and purpose of our network. Stay tuned for more.